Directional antennas are antennas that concentrate transmitted and/or received signal power in one or more directions. Differently from isotropic antennas which have uniform radiation patterns, and thus the same antenna gain in all directions, directional antennas tend to have higher antenna gain in some directions. Directional antennas can therefore be used to improve communication conditions, but only if correctly aligned with respect to, e.g., a far-end antenna.
FIG. 1 shows a schematic view of a point to point communication system according to prior art. A directional antenna 101 is here shown to be aligned with respect to a far-end directional antenna 102. An adjustment module 110a, 110b is used to steer the antenna radiation pattern, i.e., to set 111 the direction of a main lobe or to adjust an orientation of an antenna radiation pattern. The adjustment module 110a, 110b may be purely mechanical or motorized. A motorized adjustment module is possibly also adjustable by remote control.
Directional antennas, such as dish antennas, are commonly used in point-to-point radio links operating at microwave frequencies. When deploying a point-to-point radio link it is necessary, due to the narrow main lobes involved, to make sure that the antennas on each side of the radio link, i.e., near-end and far-end antennas, are oriented towards each other with sufficient degree of accuracy. If such alignment is not achieved then the radio link performance will be degraded due to loss in antenna system gain.
A commonly used method for aligning a near-end radio link antenna with respect to a corresponding far-end antenna is based on measuring received signal strength at the near-end antenna with respect to an alignment signal transmission from the far-end antenna.
Consequently, this commonly used method requires that the far-end antenna is deployed, at least coarsely aligned with respect to the near-end antenna, and is actively transmitting some type of alignment signal. The measurement of received signal strength is often done using a Volt-meter attached to a measurement port of an alignment signal receiver connected to the near-end antenna. A technician adjusts orientation of the directional antenna in an attempt to maximize received signal strength. When the technician has tested some given range of antenna directions, he selects the orientation which gave the highest received signal strength, and the antenna is then considered aligned.
Of course, a reverse procedure where the far-end antenna is instead receiving an alignment signal transmission, is also possible, but not very common.
A drawback with this commonly used alignment procedure for aligning radio link antennas is that network roll-out must be planned carefully and antennas must be aligned in a certain sequence, since each new antenna alignment procedure requires an actively transmitting and coarsely aligned antenna on the other side of the radio link against which to align. Thus, aligning directional radio antennas is cumbersome and usually involves a lot of travel between near-end and far-end antennas, in particular during network roll-out when many directional antennas should be aligned at the same time.
Hence, there is a need for improvement of directional antenna alignment techniques.